Mixing panels with different Vmp/Voc

RoySalisburyRoySalisbury Posts: 82Solar Expert ✭✭✭
I want to add more capacity to my solar setup.  Since I can no longer get the same panels that I currently have, I need to get different panels. However, they are no longer going to have the same specifications.  I'd try to stay with the same overall wattage of the panels, but the Vmp/Voc are not the same.  Currently I have 6 of the following panels:

Kyocera KD320 (320 Watt).  [Vmp - 40.1, Voc - 49.5]

These are setup with 2 in series, and 3 parallel. Going the other way would put me too close to the Voc max rating of the charge controller.

The closest that I can find form "Arizona Win/Sun" is

Silfab Solar 350 (350 watt). [Vmp - 38.9, Voc - 47.5]

When I setup a new string last time they were so far out of spec (210w vs 320w) that I setup a new charge controller just for the 6 320's.  However, that's not an option now.  I'm using an Outback MPPT charge controller (FM60 and FM80).  

My understanding is that if I put 2 more of the 350's in and hooked them in parallel, then I should be fine .. with the restriction that that all my other panels will now get degraded in voltage to the lower set.  Is that right?

If so, then I guess the 'extra' 100 watt on the new panels will make up for the loss.  Also, since the panels normally operate higher then the Vmp, that as long as the newer panels operate above 40.1, then I won't really loose anything.

this is all very confusing.  Any guidance from some experts would be appreciated.

Thanks.

Comments

  • RoySalisburyRoySalisbury Posts: 82Solar Expert ✭✭✭
    edited January 28 #2
    Just found this thread from 2012 that may be what I'm looking for.  

    http://forum.solar-electric.com/discussion/16660/panels-in-parallel-same-vmp-different-voc

    Seems to indicate that I should be fine as the MPPT will settle on the voltage and the panels will adjust the amp to accommodate.  So really should not lose anything as long as the Vmp of the lower panels does not fall below the Vmp of the higher.  

  • Raj174Raj174 Posts: 605Solar Expert ✭✭✭✭
    I think it's a good match. The output of the new string should be about the same as the others. Almost as though 320 watt panels were installed.

    Rick
    12 x 300W Renogy PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 207AH HI Power LiFePO4 no BMS, 4000W gen.
  • MichaelKMichaelK Posts: 75Registered Users ✭✭
    With a different controller you'd have more flexibility.  You could wire your Kyoceras in two arrays of 3 panels, with a Vmp of 120.3VDC.  But the open circuit voltage of three would be dangerously close to the 150Voc limit of your Outback controllers.  However, with a Midnight Classic 200 for example, you could match 3 Kyoceras wired in series to four generic grid-tie panels running at 30.1VDC.  So, 3X40.1VDC=120.3VDC≈4X30.1VDC.  One string of kyoceras would be putting out ~8.0 amps at 120.3VDC, while the second string of generics would be putting out about 8.4amps at 120.4VDC.
    15 Renogy 300w panels,  Midnight 200 CC, 8 Trojan L16 batteries, Schneider XW6848 NA inverter, AC-Delco 6000w gen.
  • littleharbor2littleharbor2 Posts: 947Solar Expert ✭✭✭✭
    edited February 22 #5
    Hyper Voc. on a Classic 150 would allow up to 174 volts(open circuit) for a 24 volt system and 198 volts (open circuit) for a 48 volt system.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.BB. Posts: 27,551Super Moderators admin
    Remember that Midnite controllers go into "safe standby" when the Vmp-array is in the "hypervolt" range (controller does not charge the battery bank during hypervolt conditions).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2littleharbor2 Posts: 947Solar Expert ✭✭✭✭
    Would that not usually be for the brief moment at daybreak while voltage is still in Voc.? It is called HyperVoc. Granted, it's not recommended to run the controller at it's limit. Just wanted to mention the extra headroom of the classics.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.BB. Posts: 27,551Super Moderators admin
    I would guess that if you had an usually cold snap, then the panel Voc-cold may be too high for the Midnite to "start"--But once the direct sun hits the panel and it begins to warm, the Voc voltage will drop to normal operating range.

    I don't think there is anything wrong with designing the system this way (you would not want to design your system to operate this way every day as you will lose some energy generation--And remember if the battery bank is disconnected for service, the Hypervolt range goes to zero until the battery is reconnected)--Just a point of information that the controller goes into standby when in Hypervolt range.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 7,702Solar Expert ✭✭✭✭
    Would that not usually be for the brief moment at daybreak while voltage is still in Voc.? It is called HyperVoc. .....
    But it's not a brief moment,  if it's cold, and some wind, the panels will stay cold and overvoltage for an hour or so, till the sun warms them up.  That is then lost harvest.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • EstragonEstragon Posts: 2,433Registered Users ✭✭✭✭
    Extreme cold plus windy in the morning is pretty rare, at least in my climate. Extreme cold tends to occur when a large high pressure area settles in, which generally brings little wind - it gets windy with lows, which brings cloud anyway. IMHO, the few times cold&windy happens is more than made up for by not having to be overly conservative in array voltage.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mike95490mike95490 Posts: 7,702Solar Expert ✭✭✭✭
    The last week, I've been tripping the overcurrent on my 60A morningstar, with an array that normally puts out about 45A  
     Cold and wind matter.   My inverter has tripped offline twice, from overvoltage, because the charge controllers can't throttle back fast enough in cold scattered clouds.

    The cold had my array delivering an extra 15A   

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • EstragonEstragon Posts: 2,433Registered Users ✭✭✭✭
    Wow. I've not seen that, but the sun is low and weak in the cold here - I don't think I've ever seen over STC rating, and it has to be extremely cold for me to get near Voc limit.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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